On 4/27/17 3:10 PM, Bob Stewart wrote:
Hi Jim,
said:"Ionosphere is one - if you're near a ionosonde you might be able to get a data set to
correlate against. It's not necessarily a "worst at noon, best at midnight" thing - some
of the satellites contributing to your fix will be on slant paths, so the solar ionization is not
uniform." Are the Ublox timing receivers a lot better at getting rid of ionospheric phase
shifts because they can see more sats than the older Motorola receivers?
And as a point of reference, the dataset I linked begins at ~9:21AM CST on
4/22/2017. I'm in west Houston, TX.
Bob
As a general thing, more satellites means more values into the average.
But it's also where they are.
If you've got a big clump of ionization to the west of you, then it
affects the satellites that are west of you, but not those that are
east. But if your current solution is more west than east, that will
pull it.
OTOH, most of the receivers also weight the contribution by the SNR. A
higher Total Electron Content (more delay) also results in more
attenuation.
1 TECU is about 16 cm in delay (call it 0.5 ns) (I think..)
typical TECU values are 50-100.. so you can see there's a pretty big effect.
ftp://ftp.ngdc.noaa.gov/STP/GPS_GNSS/Mihail's.pdf
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
